Therizinosauria

    Picture a dinosaur roughly four or five meters in length, with a stout, relatively short tail, a long, flexible neck, a short, beaked skull resembling that of a prosauropod, long arms bearing immense, sickle-like claws on each of their three fingers, two short, stout legs with broad feet bearing four functional toes each, and a big belly given additional space from the backshifting of the pubis.  This is a rough sketch of a therizinosaurian.  Is it any wonder they've been so hard to pin down taxonomically, when they display features from so many other groups plus so many unique characters of their own?  They are now known to be coelurosaurians, but it is uncertain as to which group they're closest.
    For many years, these animals were known as segnosaurids, but the discovery of Alxasaurus showed their close relationship to a bizarre theropod named Therizinosaurus, which is based on a partial arm with meter-long claws.  In the past they have been classified as strange theropods, late-surviving prosauropods, descendants of a transition from prosauropods to ornithischians, and relatives of Sauropodomorpha.  They were almost certainly herbivores, possibly equipped with "cheeks," although it was once suggested they ate fish.  Although they seem close to the oviraptorosaurians, they may not actually belong here.
    

<--Therizinosauria
      |--Falcarius
      `--+--Beipiaosaurus
           `--Therizinosauroidea
                |--Alxasaurus
                `--Therizinosauridae
                     |--Enigmosaurus
                     |--Erlikosaurus
                     |--Nanshuingosaurus
                     |--Neimongosaurus
                     |--Segnosaurus
                     `--Therizinosaurus

Therizinosauria:

Taxon or Taxa: Time\Place: Comments:
Falcarius utahensis Kirkland, Zanno, Sampson, Clark, and DeBlieux, 2005 early Aptian (EK) of Utah From the Yellow Cat Member of the Cedar Mountain Formation comes this basalmost-known therizinosaurian.  This is the one I saw at SVP in 2004 (then known as the "Crystal Geyser therizinosaurian") that convinced me that Eshanosaurus and Protognathosaurus could not be therizinosaurians.  It is known from bonebed material representing possibly thousands of individuals.  Unlike later therizinosaurians, this was a gracile animal, not too different in build from oviraptorosaurians; a cursory examination of the skeletal reconstruction puts me in mind of something like a long-tailed "Ingenia".  Its pubis did not point backward, and it lacked skull specializations like the downturning of the dentary tip or a lateral shelf on the dentary.  In fact, this animal looks to have been in transition from a carnivorous diet to an herbivorous diet.  Whatever its particular mode of feeding was, it must have been successful, given the amount of remains known for it.  
Beipiaosaurus inexpectus Xu, Tang, and Wang, 1999 mid Barremian-early Aptian (EK) of China The largest feathered classic dinosaur known from the Yixian (and the largest animal known there period), this theropod is a basal therizinosaurian.  It is known from a partial disarticulated skeleton including remains from most areas of the body.

Therizinosauria i.s.:  Skull bones from the LK of Alberta appear to belong to a therizinosaurian.  An unnamed form is known from the back half of a skeleton from the late early Turonian (LK) of Utah.

Taxon or Taxa: Time\Place: Comments:
"Chilantaisaurus" zheziangensis (N.D.) Dong, 1979 Santonian-Campanian (LK) of Mongolia This is an indeterminate therizinosaurian.  It may actually be based on part of the holotype of Nanshiungosaurus brevispinus.
Erliansaurus bellamanus Xu, Zhang, Sereno, Zhao, Kuang, Han, and Tan, 2002 early Maastrichtian (LK) of China Based on a partial skeleton including a few verts, parts of both the hip and shoulder girdle, and much limb material, Erliansaurus is described as a transitional form between the basal and derived therizinosaurids.  It is from the same area as Neimongosaurus, but is a different animal.
"Nanshiungosaurus" bohlini Dong and Yu, 1997 ?Barremian to ?Albian (EK) of China Originally referred to Nanshuingosaurus, this large therizinosaurian is currently difficult to place because of the paucity of therizinosaurian remains in general. 
Nothronychus mckinleyi Kirkland and Wolfe, 2001 middle Turonian (LK) of New Mexico Based on about a third of a skeleton of a fairly large therizinosaurian (up to 6 m), including a partial skull, several cervicals, other verts, a good chunk of the fore and hindlimbs, and an ischium once thought to be the squamosal of Zuniceratops, Nothronychus is North America's first named therizinosaurian.
Suzhousaurus megatherioides Li D., Peng C., You H., Lamanna, Harris, Lacovata, and Zhang J., 2007 EK of China A basal therizinosaurian described as more derived than Beipiaosaurus and Falcarius, but less derived than Alxasaurus, Suzhousaurus was an early large genus.  It is known from a partial postcranial skeleton, and may be closest to Nothronychus.  It may be a therizinosauroid.

Therizinosauroidea:

Taxon or Taxa: Time\Place: Comments:
Alxasaurus elesitaiensis Russell and Dong, 1993 Albian (EK) of Mongolia The discovery of several nearly complete postcranial skeletons pertaining to this beast allowed the "segnosaurids" to be classified better and showed that they were close relatives of Therizinosaurus.

Therizinosauridae:  Possible therizinosaurid embryos are known from the Santonian-Campanian (LK) of China.

Taxon or Taxa: Time\Place: Comments:
Enigmosaurus mongoliensis Barsbold and Perle, 1983 ?Santonian (LK) of Mongolia Based on a pelvis with the characteristic wideswept ilia and backwards-pointing pubis, this therizinosaurid may be synonymous with another (contemporaneous and pelvis-less Erlikosaurus has usually been the favorite speculation).
Erlikosaurus andrewsi Perle, 1980 ?Santonian (LK) of Mongolia This taxon is based on remains that include an excellently-preserved skull.  Therizinosaurian eggs from China may have been laid by this dinosaur.
Nanshiungosaurus brevispinus Dong, 1974 early Maastrichtian (LK) of China This genus was originally described as a small sauropod.  It is based on a partial vertebral column and pelvis, which is opisthopubic (given that no sauropod has ever hinted at opisthopuby, this must have made for an interesting point of discussion in the original description).
Neimongosaurus yangi Zhang, Xu, Sereno, Kuang, and Tan, 2001 early Maastrichtian (LK) of China A new long-necked therizinosaurian, Neimongosaurus preserves features like a short tail and long neck that could be shared with oviraptorosaurians.  It is based on two partial skeletons, and includes both most of the vertebral column and limb bones from a single individual, a first for a therizinosaurian; only the skull and hands are conspicuous in their absence.  The dentary is extremely deep, especially toward the front.  It was described as more derived than Beipiaosaurus, but less derived than the therizinosaurids. 
Segnosaurus galbinensis Perle, 1979 ?Santonian (LK) of Mongolia Segnosaurus was the first recognized member of Segnosauridae, remains one of the larger therizinosaurians, and displays many of their unique characteristics.
Therizinosaurus cheloniformis Maleev, 1954 early Maastrichtian (LK) of Mongolia This taxon was originally thought to be a giant turtle.  It has meter-long claws, and we can thus safely assume it was a large animal.

 

Navigation
Home Page Alphabetical Dinosaur Index Clado-Index
Background Information Glossary Faunae